1. Field of the Invention
The present invention relates to display devices and, more particularly, to light emission devices and spacers therefor.
2. Description of the Related Art
A liquid crystal display, which is one of a variety of flat panel display devices, displays an image by varying the light transmission amount at each pixel using the dielectric anisotropy property of liquid crystals whose twisting angle varies according to the voltage applied.
The liquid crystal display includes a liquid crystal panel assembly and a backlight unit for emitting light toward the liquid crystal panel assembly. The liquid crystal panel assembly displays a predetermined image by receiving light emitted from the backlight unit and transmitting or intercepting the light using a liquid crystal layer.
The backlight unit is classified according to the light source into different types, one of which is a cold cathode fluorescent lamp (CCFL) type. The CCFL is a linear light source that can uniformly emit the light to the liquid crystal panel assembly through optical members such as a diffusion sheet, a diffuser plate, and a prism sheet.
However, in the CCFL type backlight unit, since the light emitted from the CCFL travels through the optical members, there may be light loss. Considering the light loss, a relatively high intensity of light must be emitted from the CCFL. This causes an increase in power consumption. Furthermore, since it is difficult to increase the size of the CCFL type backlight unit due to structural limitations, the CCFL type backlight unit cannot be applied to large-sized display devices over 30-inch.
In addition, a light emission diode (LED) type backlight unit is also well known. The LED type backlight unit includes a plurality of LEDs and optical members such as a reflection sheet, a waveguide plate, a diffusion sheet, a diffuser plate, a prism sheet, and the like. The LED type backlight unit has a fast response time and excellent color reproduction. However, the LED type backlight unit is costly and increases the overall thickness of the display device.
Therefore, in recent years, a field emission type backlight unit that emits light using electron emission provided by an electric field has been developed to replace the CCFL and LED type backlight units. The field emission type backlight unit is a surface light source, which has relatively low power consumption and can be of large-size.
In the field emission type backlight unit, spacers are disposed between first and second substrates to endure the compression force generated by the pressure difference between an interior and exterior of a vacuum envelope. The spacers are exposed to the space along which electrons travel and thus the electrons collide with the spacers. As a result of the collision with the electrons, the spacers become electrically charged. The electrically charged spacers distort the electron beam path. In order to prevent the distortion of the electron beam path, a technology for coating a resistive layer on the surface of the spacer has been developed.
However, when the spacer coated with the resistive layer is applied to a field emission type backlight unit, it cannot endure the high voltage applied to an anode electrode and thus a short circuit may be generated between a driving electrode and the anode electrode.
As described above, conventional backlight units, including the field emission type backlight unit, have inherent problems. In addition, conventional backlight units must maintain a predetermined brightness when the display device is driven. Therefore, it becomes difficult to improve the display quality of the display device to a sufficient level.
For example, when the liquid crystal panel assembly is to display an image having a high luminance portion and a low luminance portion in response to an image signal, it will be possible to realize an image having a more improved dynamic contrast if the backlight unit can emit light having different intensities to the respective high and low luminance portions.
However, since the conventional backlight units cannot achieve the above function, improving the dynamic contrast of the image of the display device becomes limited.